It is useful to predict the characteristics of the formation or formations ahead of a bit when drilling an oil well. Such predictions allow the operator of the drilling equipment to select the bit that will best penetrate the formation or formations.
Some drilling systems include multiple cutting structures, including the bit at the end of the drill string and intermediate cutting structures, such as reamers, above the bit on the drill string. In those cases, it is possible for the intermediate cutting structures to be drilling through rock with properties that are dissimilar to the properties of the rock that the bit at the end of the drill string is cutting through.